The workshop introduces CindyJS, an open-source JavaScript framework for creating interactive mathematical visualizations on the web. Derived from the dynamic geometry program Cinderella, CindyJS brings geometric experimentation to the browser, enabling the creation of hands-on applets of geometric configurations in the projective plane and beyond. Participants will also discover CindyScript, an intuitive mathematical scripting language that integrates diverse mathematical concepts into illustrations – including GPU-based computation for real-time interactivity. Through guided examples and practical exercises, participants will learn how to build dynamic web-based visualizations from the ground up.